Varanus tsukamotoi (Kishida, 1929)

Common Name and Taxonomy

Varanus tsukamotoi, commonly known as the Mariana monitor or Saipan monitor, is a species of lizard in the Varanidae family.

Native Distribution

This species is endemic to the Northern Mariana Islands and Guam, and has been introduced to Japan in the Marshall Islands. Its native distribution includes the Mariana Islands of Alamagan, Anatahan, Cocos Island, Guam, Pagan, Rota, Saipan and Tinian, as well as Kosrae in the Federated States of Micronesia.

Introduced Populations

It is also found in the Marshall Islands on Aur and Enewetak Atolls, and in Japan; researchers think the species was brought to Japan through human introduction. A reported record of this species from Japan's Bonin Islands is considered incorrect.

Distribution Gap in Northern Mariana Islands

For reasons that are not known, this species does not occur on Sarigan in the Northern Mariana Islands island chain, even though it lives on nearby islands; the monitor species found on Sarigan is instead thought to be Bennett's long-tailed monitor (Varanus bennetti).

Reproduction and Sexual Dimorphism

In terms of reproduction, the species does not have distinct sexual dimorphism, but mature male monitors from Guam have been recorded to have three times the mass of mature females.